Electrolytic oxidation of various ores is advantageous in comparison to conventional techniques for various types of ores. For example, in one conventional process, molybdenum is recovered by a combination of multi-stage flotation techniques and roasting. However, such processing is relatively costly, the molybdenum recovery is extremely low, and the roasting of sulfide concentrate causes heavy atmospheric pollution. Similarly, the recovery of mercury has been performed by a pyrometallurgical process which constitutes a health hazard unless careful precautions are taken.
Because of the above problems, electrolytic oxidation has been employed for the recovery of mercury from mercury-bearing materials as set forth in Australian Pat. No. 464.246. There, an electro-oxidative cell is disclosed in which the slurry is directed from a common conduit into an open lower plenum chamber in direct communication with electrolytic cells formed in the spacing between multiple parallel upright electrode plates. The overflow from the plates is removed through ports connected in a common trough.
There are a number of problems created with respect to cell assemblies of the foregoing type. Firstly, the common inlet plenum for the electrolytic cells creates a major flowpath for stray voltage which reduces the electrical efficiency of the cells and thereby greatly increase the power required for the electrolytic process. Similarly, overflow of the cell is at a common outlet trough with a corresponding possibility of a stray voltage path.
A modification of such cell has been developed in an attempt to avoid excessive power consumption. There, slurry is supplied to the bottom of the cell flow path between spaced electrodes of the foregoing types through a series of spaced inlet pipes which extend across all cells. Such inlet pipes are connected to a common manifold conduit and include inlet spray-type openings for each cell.
There are many problems inherent in this modification. Firstly, it is very difficult to control this type of flow to obtain uniform pressure across the bottom of each cell. Uneven pressures cause variance in cell flow rates which creates unequal treatment for the slurry flowing through various portions of the cell. Additionally, spraying the slurry through such inlet holes causes a significant pressure drop with a corresponding high power consumption for operation of a pump.
Another problem with the modified cell is that the total volumetric flow through the cell is limited by the use of inlet holes in the pipes. Furthermore, the maximum particle size of the slurry is limited because it must pass through such openings. A further problem is that cells of the above type tend to accumulate particulate materials such as reaction products which tend to plug the openings. A system with small inlet openings of the above type is not adapted to back flushing to clean out residues in the cell.
A further problem with the above type of modified cell is that a common voltage path is presented across the various cells through the liquid in the pipes prior to entrance into the cells. Although such path is more efficient in power consumption than the cell which it replaced, a substantial power loss remains due to this voltage leakage.
A bipolar electrolytic cell for the electrolytic oxidation of sulfide ores to recover molybdenum is disclosed in U.S. Pat. No. 3,849,265. There, the slurry is illustrated as being directed to the bottom of a tank with upright electrodes forming separate cells. The inlet is through a common reservoir or plenum and so is subject to the type of power losses as set forth above with respect to Australian Pat. No. 464.246.